This invention relates to non-toxic primers in the field of small caliber ammunition. In particular, it relates to non-toxic primers which can be used in all types of small arms ammunition, including reduced energy cartridges.
Many publications and articles collected, for example, by the SAAMI (Sporting Arms and Ammunition Manufacturers"" Institute) Environmental Committee clearly indicate the necessity for environment-friendly (xe2x80x9cgreenxe2x80x9d) ammunition. The military is also moving in the same direction. For small caliber ammunition, the principal culprit in producing gaseous combustion products during firing that may be inhaled by the shooter (in the form of dust or oxides of toxic elements) is the primer. Small caliber ammunition is fired in large quantities both in indoor ranges for training or practice and outdoors for both of these reasons as well as for hunting, sporting events (trap shooting, biathlon, etc.) and military simulations.
Specifically, as detailed in the EPA (Environmental Protection Agency) list of toxic materials and the FBI (Federal Bureau of Investigation) list of toxic metals, there is a need to eliminate mercury, lead, barium, antimony, beryllium, cadmium, arsenic, chromium, selenium, tin and thallium from primer compositions. This means that long-standing chemically-stable, reliable non-corrosive primer compositions containing lead, barium, antimony or other metallic compounds are no longer acceptable from an environmental point of view. Unfortunately, primers containing such ingredients are still in wide use because suitable alternatives have not yet been found that eliminate all toxic materials as well as meeting ballistic reliability requirements and price realism.
There is much prior art. Going back to 1982, the following US patents are relevant: U.S. Pat. Nos. 4,363,679; 4,522,665; 4,566,921; 4,581,082; 4,608,102; 4,674,409; 4,675,059; 4,689,185; 4,963,201; 5,167,736; 5,353,707; 5,388,519, 5,417,160, 5,466,315 (Erickson) and U.S. Pat. No. 5,547,528 (Erickson). In addition there are European patent No 699 646 and French Patent No 9602359.
Many of these patents cite diazodinitrophenol (DDNP or dinol) as the primary explosive in combination with one or more oxidizers along with a variety of other ingredients necessary for the proper functioning of a primer. The oxidizers for primers cited in the prior art listed above include zinc peroxide, manganese dioxide, strontium peroxide, strontium nitrate, calcium carbonate, cupric oxide, ferric oxide, cesium nitrate, sodium oxalate, zirconium oxide and stannic oxide.
One oxidizer that does not appear prominently on this list is potassium nitrate (KNO3). This lack of interest is undoubtedly because KNO3 is hygroscopic (water solubility is 31.6 g/100 ml @ 20xc2x0 C.). Any primer ingredient that has a tendency to attract or absorb water is not acceptable because of the negative effect on primer ignition, which manifests itself through misfires. The two Erickson patents listed above address the question of hygroscopicity, but neither uses KNO3 as an ingredient.
U.S. Pat. No. 3,348,985 describes a gas-generating pyrotechnic composition for such uses as propellant charges for cartridges, missile propulsion, and to assist the take-off of military and commercial aircraft. This composition contains a small amount of KNO3 ( less than 9%) which is a component of the principal oxidizer in its as-purchased state and, as such, must be tolerated. U.S. Pat. No. 5,417,160 utilizes KNO3 as an oxidizer in primers, but always in combination with calcium silicide.
One way to make KNO3 immune to water (i.e., to xe2x80x9cwaterproofxe2x80x9d it) is to coat it prior to incorporation into the mix with a thin layer of nitrocellulose (NC), amounting to about 1% by weight of the formulation, as described in this invention. There is prior art unrelated to primers which describes the use of NC in formulations also containing KNO3, but not for the purposes of coating the KNO3. For example, U.S. Pat. No. 5,125,684 describes a gas-generating propellant for use in a vehicle occupant restraint system which contains KNO3 ( greater than 50% by weight) as an oxidizer and NC (20%) as a binder and principal combustion ingredient. U.S. Pat. No. 5,495,807 also deals with a gas-generating module for an airbag utilized in motor vehicles in which the gas-generating composition is arranged within a container in xe2x80x9cthe shape of a foil-like layer or coating, or alternatively consists of a granulatexe2x80x9d with a first binder of NC (2% by weight) to give consistency to the mix during kneading prior to granulation.
An objective of this invention is to find a way to utilize a hygroscopic oxidizer KNO3 as the primary and predominant oxidizer ( greater than 50% by weight of the oxidizer content) in a primer free of toxic materials in such a way that the ballistic performance of the primer will meet all performance specifications routinely required for small caliber ammunition. This will be done by demonstrating that KNO3 can be utilized as a reliable primary oxidizer if suitably coated beforehand to eliminate its hygroscopic nature.
The invention in its general form will first be described, and then its implementation in terms of specific embodiments will be detailed hereafter. These embodiments are intended to demonstrate the principle of the invention, and the manner of its implementation. The invention in its broadest and more specific forms will then be further described, and defined, in each of the individual claims which conclude this Specification.
The invention according to one aspect relies upon the presence in a primer composition of a hygroscopic oxidizer which is combined with waterproofing vapour barrier material to protect the oxidizer from undue absorption of atmospheric water vapour. A preferred oxidizer is potassium nitrate (KNO3), which is coated with nitrocellulose, as a preferred coating material to protect the KNO3 from its hygroscopic nature. Sufficient nitrocellulose coating is provided to ensure that the performance of KNO3 as an oxidizer is not degraded by the presence of water that would otherwise be absorbed by the KNO3 from the environment. Other oxidizers susceptible to moisture absorption, e.g. strontium nitrate Sr(NO3)2 can be similarly protected.
More preferably, the primer mix is free of toxic metals e.g. lead, barium, antimony. In a non-toxic primer DDNP may be employed as the primary explosive and optionally, PETN may be present as a secondary explosive. Tetrazene may be added to increase sensitivity to friction. Also optionally ZnO.ZnO2 (containing at least 50-60% of ZnO2) may be present as a secondary oxidizer, with KNO3 predominating as the principal source of oxygen.
As further preferred constituents of the primer composition, silicon carbide (carborundum) may be present to increase sensitivity to friction (i.e. as a xe2x80x9cfrictionatorxe2x80x9d) and aluminum powder may be used as the fuel.
More particularly, the preferred composition for the primer composition of the invention is shown in Table 1.